Inoculating alloy



June 1964 R. L. MICKELSON INOCULATING ALLOY Filed Aug. 10, 1962 BARIUM IN ALLOY m m m m m IE3 350 3 -INVENTOR. Robert L. Mic/re/son HIS ATTORNEYS United States Patent ""1 C 3,137,570 INOCULATING ALLOY Robert Michelson, Cambridge, Ghio, assignor to Vanadium Corporation of America, New York, N.Y., a corporation of Delaware Filed Aug. 10, 1962, Ser. No. 216,099 2 Clm'ms. (Cl. 75-424) This invention relates to a composition of matter which is capable of graphitizing cast iron in a highly effective manner.

Numerous compositions have been described in the art to cause cast iron which would ordinarily solidify white, 1.e., to solidify with a high percentage of carbides, to dissociate these carbides so that the iron solidifies grey, i.e., contains carbon in the form of graphite.

The actual mechanism underlying the change from a white solidification to a grey solidification is as yet incompletely understood although numerous theories and explanations have been advanced.

Numerous metals and alloys have been proposed for use as inoculating agents in the production of grey iron castings. The standard inoculating agents are silicon, calcium-silicon, ferro-silicon, or other silicon alloys, as well as graphite. Various degrees of etficiency are achieved by the use of these agents, and it has been attempted over the years to improve their performance. One measure of the 'efiiciency of an inoculating agent is the degree to which the iron carbide (cementite) is dissociated, resulting in the production of graphite. The direct efiect of this conversion can be seen in the depthof chill produced when the metal is cast: the deeper the chill, the greater the residual cementite in the metal; the shallower the depth of chill, the greater the conversion of cementite carbon to graphite.

A variety of problems have been encountered in connection with the use of these alloys. In some cases the use of inoculants engenders surface porosity which may be the result of aluminum when present in relatively substantial proportions in the silicon alloy. Variations in the cooling rate that occur in castings of nonuniform section size cause structural dilferences that are minimized to different degrees by standard inoculants. Some inoculants, while causing dissociation of massive carbides, allow an undersirable type of interdendn'tic graphite to precipitate. Some inoculants tend to decrease the percentage of combined carbon in pearlitic structures and thereby weaken the matrix. Also, it has been observed that certain inoculants promote undesirably large, coarse graphite flake structures in heavy sections that are slowly cooled. Iron that has relatively low percentages of carbon and silicon is generally more difiicult to inoculate properly than iron that contains higher carbon and silicon levels. The low carbon, low silicon irons are usually more prone to have massive carbides in castings of small sections. Large additions of some presently used inoculants are required to dissociate these carbides. These large additions often affect adversely the pearlitic structure and graphite size.

It is an object of this invention to provide an inoculating agent which causes the cementite in the iron to be substantially dissociated and the graphite to be evenly distributed in a beneficial manner throughout the section of the resultant casting.

It is another object of this invention to provide castings having a greatly reduced depth of chill as an indication-of the effectiveness of the inoculant of this invention.

It is a further object of this invention to provide an inoculating agent which produces the desired effects under the addition of very small amounts of this agent.

It is a further object of this invention to provide an inoculating agent which does not impair the surface quality of the castings produced.

PatentedrJune 16, 1964 Other useful objects will become apparent in the course of the following specifications.

The drawing is a graph in which the percent of barium in the alloy is plotted against the chill depth in kg".

The alloy of this invention is designed to provide a satisfactory inoculant which does not impair the surface quality of the casting and which provides satisfactory results over a wide range of sections. It is furthermore designed to develop a high strength cast iron which can be used in applications where the mechanical stresses to which the castings are exposed are considerable. Minimal additions of the inoculating agent will provide a casting which does not contain massive carbides, but which has largely graphitic carbon, along with combined carbon in a pearlitic structure. It is, however, not only important that the carbon be present as graphite, but that the graphite be present in a beneficial form. The graphite produced by the addition of the alloy of this invention is in a fine, randomly dispersed condition throughout the casting.

The effect of inoculating agents thus becomes apparent by graphitization which is amenable to measurement. Generally the effect of graphitization is measured in grey iron foundry technology by determining the amount of chill that develops during the solidification of the grey iron. This test may be performed in a number of ways. In the following specifications the test method employed has been identified by the industry-wide standard established by ASTM. In these tests, the depth of chill is inversely proportional to the effectiveness of the graphitizing treatment, i.e., the less the chill, the more effective the treatment, and vice versa. Chill is usually measured in The alloy of this invention when added to grey irons containing around.3% C, 2% Si, 0.75% Mn, 0.1% S in amounts of between two and four pounds per ton .of iron, produced a very satisfactory reduction of chill when compared with either the untreated iron or with iron treated by the more conventional graphitizing agents.

The metallic matrix developed in grey irons produced by using the alloy of this invention can be either ferritic or pearlitic in character, and thus such castings exhibit high strength, depending on the composition of the iron. In addition, the alloy renders the matrix structure less sensitive to the effects of section size. Accordingly, the mechanical characteristics of the casting are more uniform and consistent. j I

The alloy of this invention is a silicon-based composition containing auxiliary inoculating elements in a carefully balanced relationship.

The constituents of the alloy of this invention are as follows: 58-68% Si, ,912% Mn, 1.'5-4% Ca, 2.5 min. Ba, 0.81.8% Al, balance iron and incidental impurities.

In the above composition the limits of barium have been defined merely as a minimum. It has been determined as a result of extensive tests that barium above a minimum content of about 2.5% in alloys of the above composition contributes markedly to its graphitizing pow er and there is actually no specific upper limit to the effectiveness of this constituent. However, for reasons of economics, I may indicate an upper limit in the order of 15 to 20% barium in the alloy of this invention.

This point of effectiveness of barium with respect to i ,graphitizing is shown in FIGURE 1 attached hereto.

3 from FIGURE 1, the base iron had a chill depth of The graph indicates that the alloy composition without barium reduced the chill depth to The addition of 2.5% barium brought the chill down to 5% to and lowered the chill depth to Further increases in barium apparently had no additional beneficial effect, but neither was there a reversal in effectiveness. In view of these data, the barium level in the alloy of this invention is best defined as 2.5% minimum and a maximum of between 15 and The alloy of this invention is added generally in amounts of between 2 and 4 pounds per ton of iron. Occasionally the addition may range up to 15 pounds per ton. Conversely, additions on a smaller scale than 2 pounds per ton may also be made under some practices.

The following particulars will provide data relating to the performance in service of the alioy of this invention which is compared to a standard inoculating alloy designated as alloy X which is well established in the industry as a superior product.

Table I below gives the chemical composition of the two alloys used. In the following text the alloy of this invention has been designated as No. 63.

TABLE I Composition of Inoculants Alloy Si Mn Ca Ba Zr Al Fe X 59. 56 7. 02 3. 49 Nil 5. 96 1.01 Bal. 63 63. 16 9. 87 1. 20 4. 94 Nil 1. O7 Bal.

TABLE II Base Iron Composition, Percent Iron Heat. 0 I Si t Mn S 0 Eq.

The irons described in the above table were then poured into two ladles and tested. A number of ASTM type 4C chill specimens were obtained which yielded the results as shown in Table III below.

TABLE III Iron Temperature and Treatment Inoculation, Pouring 4C Chill 40 Tune. Percent Temp, F. Depth, $62" Iron Base Temp., Heat Chill I Ladle 1 Ladle 2 Laldle Lazdle X #63 1 32 2, 700 0.20 X 0.20 #63 2,610 2, 610 I8. 0 16.0 2. 30 2, 750 0.20 X 0.20 #63 2, 650 2, 620 16. 5 12. 5 3- 30 2, 750 0.20 #63 0.20 X 2, 670 2, 640 17.0 14. 0 4 27 2, 700 0.20 #63 0. 20 X 2,620 2,600 9.0 5.5 5 30 2,750 0.10 #63 0.10 X 2, 570 2,540 22.5 21. 5 6. 32 2,750 0.10 X 0. 10 #63 2,640 2,590 19.0 19. 0

It will be seen from the Table III that a very substantial reduction in the chill depth is achieved by both alloy X and alloy 63. However, the alloy of this invention shows a superiority of up to 38%, although in some cases on'y marginal advantages were observed.

T ransvcrse and Tensile Data Tensile Strength, p.s.i.

Transverse Strength, Deflection,

' 1 2" (0.750 Dia. Specimen) Lbs. (1.2" Arb. Bar) m.

Arb. Bar) Base X #63 Base X #63 From these tables again the beneficial effect of the inoculation is apparent, an effect which is most clearly demonstrated by the improvement in the deflection, i.e., the elasticity of the product. Here the improvement by the addition of inoculants is generally a factor of two, except where only a .10% addition of inoculant was made. Also in this instance, the alloy of this invention shows a marginal superiority over the standard alloy, a superiority which is reflected, with a single exception, also inthe transverse strength. In the tensile test data there is on balance a distinct advantage on the side of the alloy of this invention, although in some instances its performance was not superior to alloy X.

Table V below ofiers data on the Brinell hardness readings obtained on step castings. These castings are made to provide different section sizes and thus to give information on hardness development in depth. Since lower hardness readings are a measure of graphitization effectiveness of an inoculating alloy, these data clearly show the excellent performance of the alloy of this invention.

TABLE V Brinell Hardness of Step Castings Brincll Hardness of Sections Iron Heat 1/16 1/8 1/4" 1/2" 1" X #63 X #63 X #63 iii ii? iii? as 56:? "iii 23 234 218 214 202 184 an 552; "iii; 243 240 224 230 215 212 Section was broken off and lost in handling.

In addition to the laboratory tests, a foundry test was made using the alloy of this invention having the following composition: 63.22% Si, 10.12% Mn, 2.44% Ca, 5.37% Ba, 1.42% Al, balance Fe. Tests were carried out on acid cupola iron that had nominally 3.40% C, 2.05% Si, 0.75% Mn, 0.11% S, and 0.07% P. The base iron contained also 0.15% Cr, which was increased by the ad dition of some chrominum to 0.30%

The iron was tapped continuously into an 8-ton forehearth, poured into 2-ton transfer ladles and then distributed into l-ton pouring ladles. Inoculation took place in the transfer ladle, using a 0.4"+32 mesh alloy. The temperatures were as follows: 2840-2860 F. for the cupola spout, Q75 -277 0 F. into the transfer ladle, 2630- 2660 F. at the end of the pour. Each ton of iron required 10 minutes for pouring. Alloy X is usually used in this foundry and here it was compared with alloy #63. The results of these tests are set forth in Table VI below.

TABLE VI Final Chill, /6" Type Percent Base Test Inoculant Addition Chill,

M Transfer Start of End of Ladle Pour Pour 0.075 4 2.5 2. 5 3.0 Alloy #631- 0. 070 6 2. 5 2.0 2. 0 do .070 3 1.0 do 0. 038 7 3. 0

The above results confirm the experimental results described earlier.

I claim:

1. An inoculating alloy for grey iron, said alloy consisting essentially of 58 to 68% silicon, 9 to 12% manganese, 1.5 to 4% calcium, a minimum of 2.5% barium, and 0.8 to 1.8% aluminum, the balance being iron and incidental impurities.

2. An inoculating alloy for grey iron, said alloy consisting essentially of 58 to 68% silicon, 9 to 12% manganese, 1.5 to 4% calcium, 2.5 to barium, and 0.8 to 1.8% aluminum, the balance being iron and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS Kinzel Dec. 16, 1941 3,000,731 Ototani Sept. 19, 1961 3,033,676 COX May 8, 1962 

2. AN INOCULATING ALLOY FOR GREY IRON, SAID ALLOY CONSISTING ESSENTIALLY OF 58 TO 68% SILICON, 9 TO 12% MANGANESE, 1.5 TO 4% CALCIUM, 2.5 TO 20% BARIUM, AND 0.8 TO 1.8% ALUMINUM, THE BALANCE BEING IRON AND INCIDENTAL IMPURITIES. 